Integrated PV-thermal panel and process for production

ABSTRACT

This invention relates to producing electricity and heat by means of a hybrid solar panel. Some of the energy (about 10%) is taken off electrically at the top. The rest goes through as infrared heat to an exchange fluid below. The invention includes a means of producing photovoltaic (not just photoconductive) surfaces continuously on copper sheet substrates, without pulling or cutting conventional crystalline boules or ribbons. Significant time, labor, and cost may be saved.

BACKGROUND

Payback time for conventional photovoltaic (PV) cells is about 100years, for production of domestic electricity. Whereas, payback time forsolar heated water panels may be one tenth as much or less. Thisdisparity in cost comes from the different ways the respective energyabsorbing surfaces are processed. It is relatively easy to spray orelectroplate a copper sheet, as is done on solar heated water panels.But, as this inventor knows from personal experience, much time and manymeticulous steps are required in making PV devices. Among these stepsare orienting starter crystals, pulling crystalline boules or ribbons,cutting bulk crystals and mounting many small pieces onto panels.Accordingly, much effort has been given to making PV devices faster andcheaper, using large area teachniques: spraying, dipping, baking, etc.Unfortunately, many of these efforts have been marginal at best. Failureto establish large thin single crystals (or large grains) appears to bethe main inadequacy. Coated surfaces tend to dry amorphously or incountless tiny crystals of random orientation. Whereas, we need a singlethin crystal or at least several large grains in each PV cell. This isin order for sunlight released electrons to move in an orderly manner inthe device. The idea is to make it energetically cheaper for sunlightfreed electrons to move through an external electrical loop than throughthe semiconductor itself. Also, we want large numbers of electrons to befreed when sunlight hits the device. By themselves, intrinsicsemiconductors, such as silicon Si, do not release enough electrons tobe of interest. Si-Si bonds are strong and not broken sigfificantly bysunlight. Phosphorus (P), with its outer shell electron, is doped intosilicon, about one atom per million. This provides ample free electrons,without so many that they short out in the device instead of goingthrough the external electrical load. We also need to dope the crystalwith atoms which have a relative deficiency of electrons in their outershell. This is to provide so called " holes" into which electrons canmigrate. Boron is usually doped into silicon in about the same ratio asphosphorus. The effect is like having positively charged particles inthe electrical loop. When sunlight hits the surface, electrons (e⁻) andholes (h⁺) move in opposite directions. This creates a difference ofpotential or the equivalent of a battery in the loop, and current flowsaccordingly. This orderly movement of electrons and holes is betteroffered by a doped crystalline semiconductor than by amorphous material.Any large area production technique for making PV devices shouldendeavor to end up with this sort of final product. For related reasons,a PV cell should not be much larger than at present, namely a fewcentimeters per side. We want to produce many of these at once on alarge sheet of copper substrate. We want to circumvent seeding, growingand cutting bulk crystals and affixing large numbers of individual partsto a panel. If we can accomplish these things, considerable time andcosts may very well be saved. We want copper for a PV substrate becausethat metal works best with water or freon in conventional solar heatedpanels. We want to combine PV and regular solar thermal panels becauseabout ninety percent of solar energy goes through PV cells as infraredheat anyway. We may as well heat something besides roof shingles withthat energy.

SUMMARY OF THE INVENTION

This invention consists of a combination PV-solar heated panel. About10% of the sunlight energy is taken off the top electrically; thebalance goes through as infrared to a heat exchange fluid below. Theinvention includes a way to mass produce PV surfaces continuosly on acopper substrate without growing or cutting conventional boules orribbons or mounting numerous small pieces onto panels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of the invented hybrid PV-solar panel.

FIG. 2 shows a production line for making said panels.

FIG. 3 indicates the transition of a crystal of silicon dioxide to oneprimarily of silicon as a function of impinging hot carbon ions. FIG. 3also indicates how silicon may be bonded to copper.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 shows how the panels of this invention are fabricated. Gelatinoussilicic acid Si(OH)₄ is sprayed, brushed, or rolled onto a sheet ofclean copper or copper with a thin coat of fresh copper oxide thereon.Then the gelatinous acid is washed with hot water or steam H₂ O, thendried and ignited. The idea at this stage is to break down the silicicacid into its two constituents: silica SiO₂ (quartz) and water H₂ O.Then we want to drive off the water and leave pure crystalline silicabonded to the copper substrate. There are other ways of putting glassonto a substrate, but usually glass contains metals unwanted for ourpurposes. Then, as the SiO₂ is formed, it is to be hit by energeticcarbon atoms and ions from a combination of hot graphite rods (9, FIG.2) and carbon ion accelerators (C, FIG. 2). The idea here is to driveout oxygen atoms O and leave pure crystalline silicon Si. This is doneby forming carbon monoxide CO which is vented and burned off orchemically scrubbed by techniques discussed below. The equation is SiO₂+2C=2CO+Si. Magnesium ions could also take out the oxygen, but they tendto leave the silicon amorphous. Surface tensions from Si-O and Si-Sibonds tend to crystalize the film. Additionally, the Si film may be zonerefined by a high flux swath of energetic carbon ions from a carbon ionaccelerator (10, FIG. 2). Pure silicon crystal is bonded to randomgrained copper by means of an interfacing layer of oxygen atoms whichcontribute partly to copper oxide and partly to silicon dioxide. SeeFIGS. 3a, 3b. These layers may be regulated during production byadjusting the times, concentrations and temperatures of the materialsinvolved. Next, boron and phosphorus are baked or implanted into thesilicon crystalline sheet by means of ovens or particle accelerators.Meanwhile, a conventional thermal panel is fabricated and soldered tothe PV panel, as suggested by stations 12 and 13 of FIG. 2. SolderStation 13 also affixes electrical circuitry on the PV panel. FIG. 1shows a cross section of the final panel. In use, the panel shouldproduce about 100 watts peak power per square meter electrically andabout 900 watts peak power per square meter thermally. As forfabrication supplies, silicic acid Si(OH)₄ can be produced (along withhydrofluosilicic acid, H₂ SiF₆) by mixing water with silicontetrofluoride SiF₄, a fuming but incombustible gas. Ironically, thelatter is made by etching glass with hydrofluoric acid HF. This may seencircular. But the idea is to eliminate unwanted metals which tend tocollect in molten glass. The inventor has worked with these materials,and knows they can be handled safely, with due precautions. Theirproperties are discussed in part in many chemistry books but onlycompletely (to this inventor's knowledge) in P. J. Durrant's General andInorganic Chemistry, republished by John Wiley & Sons Inc., 1962,p412-415. A copy of this information is enclosed for the convenience ofthe Patent Examiner. This chemical information does not, however, showhow to produce photovoltaic surfaces continuously on a copper substrate.That method comes from the inventor's experience in making semiconductordevices, his training as a physicist plus the inventive process itselfwhich is difficult to define (but probably includes Murphy's law thatnothing succeeds like dumb luck!). In operation, carbon monoxide may bedissolved readily in either an ammoniacal or a hydrochloric acidsolution of cuprous chloride, resulting in the compound CuCl,CO,2H₂ O.Or it may be burned in air, with a characteristic blue flame, resultingin innocuous carbon dioxide. Which is to say, the invented procedure formaking PV surfaces can indeed be kept safe.

In more detail, FIG. 1 consists of the following components: Glazing 1(preferably clear tempered glass), Insulation-spacer 2 (to provide alayer of dead air between the often cold glazing and the energy absorberplate), Solder Lines 3, Crystalline Silicon 4 (Si), Copper Substrate 5(Cu), Embossed Tubes 6, Heat Exchange Fluid 7 (water or freon),Insulated Casing 8. Infrared heat IR is indicated going through the PVpanel into the heat exchange fluid below. Sun-released electrons e⁻ areshown migrating in one direction, holes H³⁰ in the other. Direct currentis rendered alternating by a conventional DC/AC inverter.

FIG. 2 illustrates Sheet Copper Roll 5b, Silicic Acid Si(OH)₄, Hot Wateror Steam H₂ O, Hot Graphite Rods 9, Silica Film SiO₂, SiliconCrystalline Film Si, Carbon Monoxide CO vented to CO Scrubber 15, CarbonIon Accelerator C, Zone Refined Strip 10, Boron Implanter B, PhosphorusImplanter P, Sheet Copper Roll 11, Embossed Tube 11a, Embosser 12,Solder Station 13, Conveyor 14.

FIG. 3a indicates the crystalline structure of silica SiO₂, its bondingto Copper Substrate Cu by Oxygen Atoms O. FIG. 3b indicates apredominantly pure Silicon Si crystal after Carbon Atoms or Ions C haveremoved most of the crystal's oxygen by forming carbon monoxide.

The inventor claims:
 1. An integrated photovoltaic-thermal panelcomprising a layer of crystalline silicon made in part by reduction ofsilicic acid by hot carbon atoms and having a p-n junction therein, on asubstrate of oxidized copper.
 2. A process for production of integratedphotovoltaic-thermal panels, the preferred process including thefollowing chemical vapor depositions, in air, and the following workstations:(a) copper oxide station, whereby sheet copper, Cu, is cleanedand a layer of copper oxide, CuO, is formed thereon by heating saidcopper in air or steam, (b) silica station, whereby silicic acid,Si(OH)₄, and steam, H₂ O, are sprayed on said hot oxidized sheets ofcopper, and Si(OH)₄ is reduced by hot carbon atoms to carbon monoxide,CO, which is vented and burned off, and silica, SiO₂, a layer of whichis deposited onto and bonded thermally to said copper oxide layer, (c)silicon station, whereby said silicic acid is further reduced byincreased numbers of hot carbon atoms to silicon, Si, a layer of whichis deposited on and bonded to said SiO₂ layer, (d) p-n junction station,whereby boron atoms, then phosphorus atoms, are diffused into saidsilicon layer, under temperature, timing and number density controls, toestablish what is called a p-n junction, (e) crystallization station,whereby heat is applied to the surface of said doped silicon layer, tosinter same and to let silicon atoms form bonds with one another in anorderly and crystalline manner and dominate over unordered, amorphous,bonds of oxide layers below, the results being a crystallinephotovoltaic, PV, surface layer bonded to a silica layer and that to CuOand that to Cu, (f) electrode grid station, whereby electrical leadwiresare affixed in series and in parallel to said PV surfaces, (g) thermalexchanger station, whereby flat tubes are soldered to the underside ofsaid copper substrate, to carry a heat exchange fluid to and away fromsaid PV layer, to cool said PV layer and to extract thermal heat as wellas electrical energy from said integrated PV-thermal panel.